The invention relates to an automotive electrical machine, and particularly to an alternator having a finned stator sleeve adapted to channel liquid coolant axially through the alternator to cool the alternator.
This invention is related to an electrical alternator, particularly adapted for use in motor vehicle applications including passenger cars and light trucks. These devices are typically mechanically driven using a drive belt wrapped on a pulley connected to the crankshaft of the vehicle""s internal combustion engine. The belt drives a pulley on the alternator which rotates an internal rotor assembly to generate alternating current (AC) electrical power. This alternating current electrical power is rectified to direct current (DC) and supplied to the motor vehicle""s electrical bus and storage battery.
While alternators have been in use in motor vehicles for many decades, today""s demands on motor vehicle design, cost, and performance have placed increasing emphasis on the design of more efficient alternators. Today""s motor vehicles feature a dramatic increase in the number of electrical on-board systems and accessories. Such electrical devices include interior and exterior lighting, climate control systems; increasingly sophisticated powertrain control systems, vehicle stability systems, traction control systems, and anti-lock brake systems. Vehicle audio and telematics systems place further demands on the vehicle""s electrical system. Still further challenges in terms of the output capacity of the motor vehicle""s electrical alternators will come with the widespread adoption of electrically assisted power steering and electric vehicle braking systems. Compounding these design challenges is the fact that the vehicle""s electrical system demands vary widely, irrespective of the engine operating speed which drives the alternator and changes through various driving conditions.
In addition to the challenges of providing high electrical output for the vehicle electrical alternator, further constraints include the desire to minimize the size of the alternator with respect to under hood packaging limitations, and its"" mass which relates to the vehicle""s fuel mileage.
In addition to the need of providing higher electrical output, designers of these devices further strive to provide high efficiency in the conversion of mechanical power delivered by the engine driven belt to electrical power output. Such efficiency translates directly into higher overall thermal efficiency of the motor vehicle and thus into fuel economy gains. And finally, as is the case with all components for mass-produced motor vehicles, cost remains a factor in the competitive offerings of such components to original equipment manufacturers.
One concern with higher power producing alternators is heat production. Fans mounted on the rotor or pulley of the alternator will circulate air to cool the alternator, however, with higher output alternators, there is too much heat produced to be dissipated by these fans. Liquid cooled alternators dissipate the heat more effectively, but require extra size to accommodate cooling flow channels. Liquid cooled alternators further offer the benefit of running quieter than air cooled alternators, a desired feature as designers seek to reduce overall vehicle noise.
Therefore, there is a need for an alternator having improved conductive cooling features that allow liquid coolant to flow through the alternator while still maintaining a small compact size.
In a first aspect of the present invention, an alternator includes an inner housing assembly, an outer housing mounted over the inner housing assembly. O-rings positioned between the inner housing assembly and the outer housing define a sealed liquid coolant flow chamber having an inlet reservoir, an outlet reservoir, and a cross over reservoir. The inner housing assembly includes a stator sleeve having a plurality of radially extending axial fins which extend outward to contact the inner surface of the outer housing to define a plurality of axial flow channels. A first portion of the flow channels interconnects the inlet reservoir to the cross over reservoir, and a second portion of the flow channels interconnects the cross over reservoir to the outlet reservoir.
The inlet and outlet reservoirs are defined by opposing first and second disk shaped portions of the inner housing spaced apart from one another to form a disk shaped cavity extending diametrically across the alternator. A divider extend across and divides the disk shaped cavity into the inlet reservoir and the outlet reservoir.
An inlet extends from the inlet reservoir and is adapted to allow liquid coolant to enter the inlet reservoir. An outlet extends from the outlet reservoir and is adapted to allow coolant to exit the flow chamber. Coolant entering the flow chamber flows from the inlet reservoir axially through the flow channels to the cross over reservoir. From the cross over reservoir the coolant then flows axially through the flow channels to the outlet reservoir.
In another aspect of the present invention, the inlet and the outlet are adapted to connect to a coolant system of an automobile such that engine coolant is circulated through the electric machine.
In still another aspect of the present invention, the alternator comprises a shaft rotatably supported within the inner housing assembly by a pair of bearing elements, having a pulley mounted to a first end and a pair of slip rings mounted to a second end. A rotor assembly, including first and second pole pieces, is mounted onto the shaft with an excitation winding mounted between the first and second pole pieces and a stator assembly is fixedly mounted within the inner housing in functional engagement with the rotor assembly.
Additional benefits and advantages of the present invention will become apparent to those skilled in the art to which the present invention relates from the subsequent description of the preferred embodiment and the appended claims, taken in conjunction with the accompanying drawings.